DESCRIPTION(adapted from applicant's abstract): The mission that underlies this research is to understand the nature of computations that take place in the human brain to give rise to perception and higher brain function. Can one deduce cortical circuits or processing stages underlying perception? Can we infer the specific consequences of focal brain damage and suggest that what remedies might be possible? A fruitful avenue for addressing this mission is to use an animal model in which careful investigations can be made at the single neuron level. The research focuses on lightness perception and its underlying mechanisms as well as related investigations into the representation of visual information in neural responses. Lightness perception is of considerable behavioral significance for object recognition, but little is known about its neural basis. It is an ideal probe for investigating the link between perception and neural activity because its perception is highly context dependent and classic visual demonstrations and illusions involving lightness are compelling. The strength and malleability of lightness effects suggests that there may be robust context-dependent neural activity that can be studied to clarify how perception depends on the activity of single neurons and populations of neurons. The research will assess the consistency between single cell responses and the key elements of lightness perception including lightness constancy and anchoring. Recordings will be made across several ventral areas of visual cortex to determine which area(s) contain surface representations and whether a surface representation is constructed at one stage or across multiple stages of processing. Experiments will quantify the relative timing of neural responses to assess the relationship between perceptual demonstrations of filling-in and possible underlying mechanisms. They will also characterize the manner in which stimulus information is represented in the delayed responses of cortical neurons and investigate preliminary findings of "top down" signals in area V1.